The only thing I can suggest is letting the upper management know. I was in one situation, many years ago, when I was teaching a group class in SF for a NYC-based company. I happened on a very difficult female student. Usually my students would love my teaching methods and be enthusiastic, but she took everything from a very negative angle. I immediately called the head of the company in NYC and told him everything. By then I had had numerous stellar student evaluations, and the head of the company had respect for me.

So when eventually this difficult student wanted to cancel her class (it was a 9 session class) and called the head of the company to complain, it was not as if she were dropping a bomb - he was prepared, having by then heard my side of the story, told in dispassionate, objective terms. He later told me that I did the right thing notifying him as soon as I ran into that problem.

So the takeaway basically is that when YOU are the one escalating an issue to the upper management, YOU also get to define the issue and speak your mind. YOU are being proactive, which is far easier than trying to do the right thing reactively.

This is probably all extraneous because all your coworkers have supported you, but if you have upper management - well, one idea is to escalate to them and let them how about the stupid b!!itch.

I have a feeling that in customer interactions roles, coworkers bond with one another and band together when there is an obnoxious client. It sounds like this was the case at your place of employment.